Controlling device for compressors



May 28, 1957 P. A. YERG ER 2,793,803

CONTROLLING DEVICE FOR COMPRESSORS Filed Aug. 12, 1954 OFF 48 AUTO. F CONSTANT CONTROL s ar-:0 50

as 3: I58 I56 73 6 74 79 :35 82 58 I52 206 q l88 202 7 W406 72 4o 0 :7 76 8 I I7 2 5 7 6O 56 |48 m 22 92 I64? I 1 94 INVENT CR PAUL A- YERGER HIS ATTORNEY 2,793,803 CONTROLLING onvrcn non coMPREssoRs Paul A. Yerger, Bloomsbury, N. 1., assignor to Iugersoll- Rand Company, New York, N. Y., a corporation of New Jersey Application August 1.2, 1954, Serial No. 449,406

6 Claims. (Cl. 230-6) This invention relates to compressors, and more particularly to an improved controlling device for compressors having force-feed lubrication.

It is common practice to control the output of a compressor according to the variation in discharge pressure by means of so-called dual-control, as, for example, constant-speed control and automatic start-stop control in a single unit, in which is also provided means for selecting the type of control to be used in accordance with the demand for air.

In many units of this type a three-way valve is used for controlling the operation of the compressor-unloading valves and is actuated by a pressure-operated valve which acts responsively to changes in discharge pressure. It is also used in conjunction with a pneumatically or electrically-actuated time-delay device to insure an unloaded condition of the compressor until the motor attains normal speed.

As heretofore constructed, none of these dual-control units having an electric time-delay switch includes safety devices for emergency shut-down of a compressor with force-feed lubrication in the event of lubricating oil pressure failure or an abnormal thermal condition of the fluid discharged by the compressor.

Therefore, an object of my invention is to include in the control circuit of a compressor having force-feed lubrication, means for preventing damage to said compressor which may be caused by the failure of lubricating oil pressure or resulting from excessive discharge-fluid temperature. I

Other objects will be pointed out in the following description of the accompanying drawing, which illustrates a preferred embodiment of the invention and is a side elevation of the compressor and an electric dualcontrol circuit therefor, shown diagrammatically and partly broken away.

Referring to the drawing, the invention is shown as applied to a single stage compressor 20, although it could be applied to any type of compressor. The compressor has a gear-driven oil pump 21 and is driven by an electric motor 22 by means of a belt 24 and pulleys 26 and 28 on the motor and the compressor, respectively. The motor 22 receives its power through a three-phase power line 29 having leads 1, 2 and 3, and air enters the cylinder 30 of the compressor through an intake port 32 and is discharged under pressure through a pipe 34 to a receiver 36.

The control circuit, designated 37, for the compressor includes a normally-closed pressure-actuated switch 38, which is responsive to variations of air pressure in the receiver 36 to control a solenoid-operated three-way valve 40 for operating free-air unloaders, only the covers 42 of which are shown, to unload the compressor 20. Directly associated with the three-way valve 40 is a time-delay relay 44, which delays the loading of the compressor 20 upon starting and is actuated simultaneously with a solenoid-operated line starter switch assembly 46 in the line 29 for controlling the motor 22. Completing the "ice circuit is a manually operated selector switch 48 for determining the type of control to be used.

In accordance with the practice of the invention, a mechanically-latched relay 50 acting as a circuit breaker is inserted in the starter'switch circuit for shutting down the motor 22, whenever energized by an oil pressure switch 52 which acts responsively to a failure of the lubricating oil pressure or by a thermal switch 54 which acts responsively to an abnormal temperature condition in the fluid discharged by the compressor.

The pressure switch 38 is normally closed and is known commercially as a Mercoid switch. It is connected to the receiver 36 by piping 56, and opens the control circuit at a predetermined maximum discharge pressure and closes it at a predetermined minimum pressure, thereby acting as a pilot switch for the control circuit 37.

Piping 56 conveys pressure fluid from the receiver 36 to the valve '40 and is threadedly connected to the body 58 thereof. It opens into an inlet chamber 60 in the lower portion of the body, which, in addition, has a discharge chamber 62 in its upper portion and a transfer chamber 64 between the chambers 68 and 62. The discharge chamber 62 has an exhaust port 66 communicating said chamber with the atmosphere. Threadedly connected to the body 58 is piping 68 for conveying pressure fluid from the transfer chamber 64 to the free-air unloader covers 42 on cylinder 30.

Connecting the inlet chamber 60 and the transfer chamber 64 is a port 70 having a beveled valve seat 72 at its juncture with the chamber 60. Likewise, the discharge chamber 62 and the transfer chamber 64 are connected by a port 73 having a valve seat 74 at its juncture with the chamber 62. The ports 70 and 73 are alternately opened and closed by a two-headed valve 76 which is actuated by a solenoid 78, the core 79 of which interlockingly engages an end of a lever 80, which is pivotally connected to .the body 58 at its other end and to a stem 82 of the valve 76 at an'intermediate point. Springs 84 and 85 are positioned in the discharge chamber 62 and in the inlet chamber 60 between the upper and lower heads of the valve 76 and two caps 86 and 87 screwed into the body 58, respectively.

The resistance of the springs 84 and 85 and the weight of the solenoid core 79 and the lever 80 are such that, when the solenoid 78 is deenergized, the valve 76 is held in position to cover the port 73 and to uncover the port 70, thereby admitting receiver pressure to the free-air unloaders through the piping 68. When the solenoid 78 is energized, the valve 76 is shifted thereby to its other limiting position and cuts off the receiver pressure to the free-air unloaders and establishes communication between the chambers 64 and 62 for exhausting the fluid from the compressor unloaders.

Electrically connected to the solenoid 78 is the timedelay relay 44. The relay 44 consists of a casing 90, which houses a coil 92 encircling a core 94. The core 94 carries a piston 96 at its lower end to reciprocate in a cylinder 98 at the lower end of the casing 98. In the side Wall of the cylinder 98 is a restricted passage 102 communicating with the opposite ends of the cylinder 98. The piston 96 contains la ball check valve 104 which serves to prevent flow of a fluid, such as oil, through the piston 96 in the downward direction but allows relatively free flow in the upward direction. This cylinder construction constitutes a Well known dash-pot, which is used to retard the upward motion of the core 94 upon energizaticn of the coil 92 for closing contacts 106 by means of a switch arm 108 pivotally connected to th upper end of the. core 94.

The starter switch assembly 46 is of conventional construction and comprises a manually-operable switch 110 and an electrically operated switch 112. The switch 112 water pressure, a break in the water line or leaky fittings. It could also be caused by the heat of friction developing between the piston and the cylinder due to the lack of lubrication. When such a condition occurs, the thermal switch 54 may act before the oil pressure switch 52 acts to stop the motor 22 and the compressor 20.

It is to be understood that, although switches 52 and 54 can act independently of each other, they may also act at or near the same time to effect the cutting oif of the power supply to the motor 22, whenever the conditions controlling the operation of said switches prevail in the compressor.

I claim:

1. The combination of a compressor having forcefeed lubrication, an electric driving motor for the compressor, an electric control circuit for the compressor, electrically actuated load-controlling means in the circuit for loading and unloading the compressor, an electrically actuated starter switch in the circuit for controlling the flow of power to the motor, pressure responsive means in said circuit connected to the compressor discharge and operatively associated with the starter switch for starting and stopping the motor in response to predetermined minimum and maximum discharge pressures respectively, an electrically actuated circuit breaker in the circuit, an oil pressure switch in the control circuit operatively associated with the circuit breaker and acting responsively to a predetermined minimum compressor lubricating oil pressure for energizing the circuit breaker to open the control circuit, and an electrically actuated time delay device in the circuit energized simultaneously with the starter switch and connected to delay the load-controlling means in loading the compressor upon starting thereof until it attains a predetermined speed and connected to prevent the oil pressure switch from energizing the circuit breaker before the loading-controlling means acts to apply the load to the compressor upon starting thereof.

2. The combination as stated in claim 1 in which a thermally responsive switch in the control circuit is also operatively associated with the circuit breaker and acts responsively to a predetermined maximum compressor discharge temperature for energizing the circuit breaker to open the control circuit.

3. The combination of a compressor having forcefeed lubrication, an electric driving motor for the compressor, an electric control circuit for the compressor, electrically actuated load-controlling means in the circuit for loading and unloading the compressor, an electrically actuated starter switch in the circuit for controlling the flow of power to the motor, pressure responsive means in said circuit connected to the compressor discharge and operatively associated with the load-controlling means for loading and unloading the compressor in response to predetermined minimum and maximum discharge pressures respectively, an electrically actuated circuit breaker in the circuit, an oil pressure switch in the control circuit operatively associated with the circuit breaker and acting responsively to a predetermined minimum compressor lubricating oil pressure for energizing the circuit breaker to open the control circuit, and an electrically actuated time delay device in the circuit energized simultaneously with the starter switch and connected to delay the load-controlling means in loading the compressor upon starting thereof until it attains a predetermined speed and connected to prevent the oil pressure switch from energizing the circuit breaker before the loadcontrolling means acts to apply the load to the compressor upon starting thereof.

4. The combination as stated in claim 3 in which a thermally responsive switch in the control circuit is also operatively associated with the circuit breaker and acts responsively to a predetermined maximum compressor discharge temperature for energizing the circuit breaker to open the control circuit.

5. The combination of a compressor having force-feed lubrication, an electric driving motor for the compressor, an electric control circuit for the compressor, electrically actuated load-controlling means in the circuit for loading and unloading the compressor, electrically-actuated starter switch means in the circuit for starting and stopping the motor, pressure responsive means in said circuit in communication with the compressor discharge and connected to control both the starter switch means and the loadcontrolling means in response to predetermined maximum and minimum discharge pressures, a manually operable switch in the circuit connected to selectively render the pressure responsive means efiective to control one of said starter switch and load-controlling means, an electrically actuated circuit breaker in the circuit, an oil pressure switch in the control circuit operatively associated with the circuit breaker and acting responsively to a preetermined minimum compressor lubricating oil pressure for energizing the circuit breaker to open the control circuit, and an electrically actuated time delay device in the circuit energized simultaneously with the starter switch and connected to delay the load-controlling means in loading the compressor upon starting thereof until it attains a predetermined speed and connected to prevent the oil pressure switch from energizing the circuit breaker before the load-controlling means acts to apply the load to the compressor upon starting thereof.

6. The combination as stated in claim 5 in which a thermally responsive switch in the control circuit is also operatively associated with the circuit breaker and acts responsively to a predetermined maximum compressor discharge temperature for energizing the circuit breaker to open the control circuit.

References Cited in the file of this patent UNITED STATES PATENTS 1,606,060 Cox Nov. 9, 1926 1,785,979 Sanford Dec. 23, 1930 1,786,278 Wilson Dec. 23, 1930 1,786,367 Sanford Dec. 23, 1930 1,834,600 Wineman Dec. 1, 1931 1,863,851 Hughes June 21, 1932 1,952,299 Van Valkenburg Mar. 27, 1934 2,065,204 Aikman Dec. 22, 1936 2,137,221 Aikman Nov. 22, 1938 2,461,076 Neeson Feb. 8, 1949 2,665,053 Bancel Jan. 5, 1954 

